Conventional magnetic return paths for accelerometers, such as the accelerometer shown in FIGS. 1 and 2, create a flux distribution in an air gap that interacts with a coil that is attached to a flexible proof mass. The flux interacts with the current in the coil to produce a rebalance force proportional to the acceleration to which the device is subjected. The flux density across the air gap is not uniform given geometric constraints of constructing useful circuits. Further, the field strength of a magnetic circuit is not constant when it interacts with the coil with changing direction of current flow. The field strength follows the minor loop slope of the magnet. If the device is subjected to vibration which can change the orientation of the coil with respect to the flux and the amplitude of the flux itself, the output of the device will change independent of the acceleration being measured. This error is called vibration rectification. For any given magnetic circuit, there is an optimum location of the coil in the field to minimize this effect. Means have been developed to cope with this problem using spacers located between the coil and the proof mass. The spacers increase the pendulosity, add cost and increase the difficulty of manufacturing. Also, the desire to minimize the output change under vibration has lead to the development of short coils that need to be extremely clean and uniformly manufactured to avoid contact with the components that define the air gap.
Therefore, there exists a need to simplify the manufacturing and reduce the cost and complexity of interacting with the flux distribution in accelerometers of this type.